[helpers] add missing helpers

[Hebilicious]

Describe the feature

Some helpers that are missing from h3, and require users to explicitly rely on event.node.

We should provide the following helpers as a part of the migration to #73

Once everything is covered, we can start deprecating event.node usage for end-users, as they should not rely on node agnostic API for their needs.

Header :

• removeResponseHeaders
• removeResponseHeader
• getRequestRawHeader
• getResponseHeaders
• getResponseHeader

Response :

• sendResponse

URL :

• setOriginalUrlPath
• getOriginalUrlPath
• setUrlPath
• getUrlPath
• getRequestPath

Note specific :

• nodeResWritableEnded (event.node.res.writableEnded)

Reference for implementation and test https://github.com/Hebilicious/h3/pull/2/files

Additional information

• Would you be willing to help implement this feature?

[pi0]

I think now we have most missing utils as event.[] props. Let's see what is missing in the future.